Real-time component monitoring and replenishment system for multicomponent fluids

ABSTRACT

A multicomponent fluid composition monitoring and compositional control system, in which a component analysis is effected by titration or other analytical procedure, for one or more components of interest, and a computational means then is employed to determine and responsively adjust the relative amount or proportion of the one or more components in the multicomponent fluid composition, to maintain a predetermined compositional character of the multicomponent fluid composition. The system is usefully employed in semiconductor manufacturing photoresist and post-etch residue removal, in which the cleaning medium is a semi-aqueous solvent composition, and water is the monitored and responsively adjusted component.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a real-time fluid monitoringand concentration control system for maintaining concentration of one ormore selected species in multicomponent fluids at a desired level, e.g.,in a range defining effective or optimal operation.

2. Description of the Related Art

In the field of semiconductor manufacturing, a number of multicomponentfluids are employed to carry out process operations, including etching,chemical mechanical planarization (CMP), photolithography, chemicalvapor deposition, spin-on coatings application, supercritical fluidscleaning operations, wafer solvent drying operations, to name a few.

In many of these process steps, the relative concentrations orproportions of various components in the multicomponent process fluidmust be maintained at a predetermined value or within a selected range,in order to achieve satisfactory results and avoid the necessity ofrework or discarding of defective semiconductor device structures,including finished devices as well as precursor structures thereof.

By way of specific example, in semiconductor manufacturing operations ofphotolithography and etch processes, various solvents are employed forphotoresist and post-etch residue removal.

Photoresist compositions are solvent-based, light-sensitive solutions,which are uniformly applied to a semiconductor wafer and then processedto leave a selected pattern of cured photoresist on the wafer afterdevelopment. Etching then is carried out, wherein reactive gases orliquids are used to remove undesired material from the wafer surface, inthe areas where the material is not protected by the cured photoresist.

During etching, various chemical complexes are formed or remain onhorizontal and vertical surfaces of the structures being delineated. Atthe completion of the etch process, these complexes are no longernecessary and need to be removed, together with any remaining cured oruncured photoresist. This is typically accomplished using a mixture offluids in gaseous, liquid or supercritical state or a combinationthereof. Solvent mixtures used for the liquid removal of the curedphotoresist and post-etch residues from the wafer include both acidic aswell as basic solvent compositions.

The ability of the solvent chemistry to remove the cured photoresist andpost-etch residues is strongly dependent on the ratios of itscomponents. In addition, many solvent components require an elevatedoperating temperature to be effective. However, in solvent systems wherewater is a component, heating the solvent causes the water to evaporate.If not enough water is present in these solvent systems, then thesolvent can become ineffective. Conversely, if too much water ispresent, damage may occur to exposed surfaces on the wafer. Therefore,an out-of-specification solvent mixture can result in severe damage tothe wafers and/or a failure to remove undesired materials such as thephotoresist or etch-generated residues.

In addition to process instability, significant costs can be incurreddue to the limited lifetime of these solvent mixtures. These canvariously include: costs of the chemicals; costs associated withequipment downtime reducing the production efficiency of themanufacturing facility; costs associated with an incremental and/orcatastrophic yield loss due to device parametric failures of defectivewafers resulting from use of out-of-specification chemicals, anddisposal costs of the high volumes of required chemicals.

The problems attendant the use of out-of-specification multicomponentsolvent compositions in removal of photoresist and post-etch residuesare illustrative of the difficulties encountered in many industrialprocesses in which compositional uniformity of a multicomponent fluidcomposition is critical to meeting process objectives and commercialviability.

The foregoing provides a background to the advance of the presentinvention, as described more fully hereinafter.

SUMMARY OF THE INVENTION

The present invention relates in one aspect to a multicomponent fluidcomposition monitoring and compositional control system, in which acomponent analysis is effected by titration or other analyticalprocedure, for one or more components of interest, and a computationalmeans then is employed to determine and responsively adjust the relativeamount or proportion of the one or more components in the multicomponentfluid composition, in order to maintain a predetermined compositionalcharacter of the multicomponent fluid composition.

In a further specific aspect, the multicomponent fluid compositionmonitoring and compositional control system is utilized in a fluid-usingprocessing facility, and arranged for real-time component analysis ofthe multicomponent fluid, with the computational means determining andresponsively adjusting the relative amount or proportion of thecomponent(s) in the multicomponent fluid composition, in real time, tomaintain the predetermined compositional character of the multicomponentfluid composition in the fluid-using processing facility.

A further aspect of the invention relates to a fluid utilization andmanagement system, comprising a fluid-using processing facility using amulticomponent fluid, and a fluid monitoring and concentration controlsystem for maintaining concentration of one or more selected species inthe multicomponent fluid at a desired level for use of themulticomponent fluid in the fluid-using processing facility, wherein thefluid monitoring and concentration control system comprises (i) ananalyzer unit, constructed and arranged to monitor the concentration ofone or more components of the multicomponent fluid using a real-timemethodology, and (ii) a control unit constructed and arranged to comparethe results of the analyzer unit to pre-programmed specifications andresponsively control dispensing of the aforementioned one or morecomponents into the multicomponent fluid as required to maintain apredetermined concentration of the aforementioned one or more componentsin the multicomponent fluid used in the fluid-using processing facility.

A further aspect of the invention relates to a system for generatinghydrogen peroxide at a point of use comprising a hydrogen peroxide-usingprocessing facility, such system comprising an electrochemical cellconstructed and arranged for generating hydrogen peroxide, and ahydrogen peroxide monitoring and concentration control assemblyincluding a Karl Fischer analysis unit comprising means for samplingfluid from the electrochemical cell and analyzing same by Karl Fischeranalysis, wherein the hydrogen peroxide monitoring and concentrationcontrol assembly includes a source of titration agent for the KarlFischer analysis, and means for real-time determination of concentrationof the hydrogen peroxide based on the Karl Fischer analysis.

Yet another aspect of the invention relates to a system for generatinghydroxylamine at a point of use comprising a hydroxylamine-usingprocessing facility, such system comprising an electrochemical cellconstructed and arranged for generating hydroxylamine, and ahydroxylamine monitoring and concentration control assembly including aKarl Fischer analysis unit comprising means for sampling fluid from theelectrochemical cell and analyzing same by Karl Fischer analysis,wherein the hydroxylamine monitoring and concentration control assemblyincludes a source of titration agent for the Karl Fischer analysis, andmeans for real-time determination of concentration of the hydroxylaminebased on the Karl Fischer analysis.

A still further aspect of the invention relates to a system forgenerating an active reagent selected from hydroxylamine and hydrazineat a point of use including a semiconductor manufacturing facilityarranged for use of the active reagent, in which the system includes (i)means for electrochemical generation of the active reagent at the pointof use, (ii) means for simultaneous real-time process monitoring of theconcentration of these chemicals both in the electrochemical cell and atthe point of use, such means (i) and (ii) including a Karl Fisherelectrochemical cell platform for both the generation and monitoring ofthe active reagent.

In another aspect, the invention relates to a multicomponent fluidcomposition monitoring and compositional control system, including meansfor performing component analysis of the multicomponent fluid bytitration or other analytical procedure, for one or more components ofinterest, and computational means constructed and arranged to determineand responsively adjust the relative amount or proportion of the one ormore components in the multicomponent fluid composition, to maintain apredetermined compositional character of the multicomponent fluidcomposition.

In another aspect, the invention relates to a process of monitoring andcompositionally controlling a multicomponent fluid used in a processingfacility, such process including conducting a real-time componentanalysis of the multicomponent fluid by titration or other analyticalprocedure, for one or more components of interest, and computationallyand responsively adjusting in real time the relative amount orproportion of the one or more components in the multicomponent fluidcomposition, to maintain a predetermined compositional character of themulticomponent fluid composition utilized in the fluid-using processingfacility.

Another aspect of the invention relates to a fluid utilization andmanagement process, including providing a fluid-using processingfacility using a multicomponent fluid, and maintaining concentration ofone or more selected species in the multicomponent fluid at a desiredlevel for use of the multicomponent fluid in the fluid-using processingfacility, by monitoring the concentration of one or more components ofthe multicomponent fluid using a real-time methodology, and comparingthe results of the methodology to preestablished specifications andresponsively controlling dispensing of said one or more components intothe multicomponent fluid as required to maintain a predeterminedconcentration of the aforementioned one or more components in themulticomponent fluid used in the fluid-using processing facility.

In yet another aspect, the invention relates to a process for generatinghydrogen peroxide at a point of use including a hydrogen peroxide-usingprocessing facility, such process including generating hydrogen peroxidein an electrochemical cell, and monitoring hydrogen peroxide in a KarlFischer analysis unit including sampling fluid from the electrochemicalcell and analyzing same by Karl Fischer analysis, titrating hydrogenperoxide in the sampling fluid with titration agent in the Karl Fischeranalysis, and determining in real time the concentration of the hydrogenperoxide based on the Karl Fischer analysis.

A further aspect of the invention relates to a process for generatinghydroxylamine at a point of use including a hydroxylamine-usingprocessing facility, such process including generating hydroxylamine inan electrochemical cell, and monitoring and controlling concentration ofthe hydroxylamine, including sampling fluid from the electrochemicalcell and analyzing same by Karl Fischer analysis, wherein thehydroxylamine monitoring and concentration control steps includereal-time determination of concentration of the hydroxylamine based onthe Karl Fischer analysis.

Yet a further aspect of the invention relates to a process forgenerating an active reagent selected from hydroxylamine and hydrazineat a point of use including a semiconductor manufacturing facilityarranged for use of the active reagent, such process including (i)electrochemically generating the active reagent at the point of use,(ii) simultaneously monitoring concentration of the active reagent inreal time, both in the electrochemical cell and at the point of use,using a Karl Fisher electrochemical cell platform for both thegeneration and monitoring of the active reagent.

Another aspect of the invention relates to a multicomponent fluidcomposition monitoring and compositional control process, includingperforming component analysis of the multicomponent fluid by titrationor other analytical procedure, for one or more components of interest,and computationally determining and responsively adjusting the relativeamount or proportion of the one or more components in the multicomponentfluid composition, to maintain a predetermined compositional characterof the multicomponent fluid composition.

Other aspects, features and embodiments of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a fluid component monitoring andconcentration maintenance system according to one embodiment of theinvention.

FIG. 2A is a schematic representation of the fluid component monitoringand concentration maintenance system of FIG. 1, as wall-mounted in asemiconductor manufacturing facility utilizing wall mounting brackets.

FIG. 2B is a schematic representation of a fluid component monitoringand concentration maintenance system according to a second embodiment ofthe invention utilizing a single, self-contained cabinet for mountingthe system, in which the cabinet optionally may be equipped with wheelsto facilitate relocation as a mobile system within a semiconductormanufacturing facility or alternatively the cabinet may be fabricatedwithout wheels to provide a semi-permanent installed system that isfixedly positioned in the semiconductor manufacturing facility.

FIG. 3 shows an illustrative arrangement of the fluid componentmonitoring and concentration maintenance system with a fast looprecirculating bath arrangement utilizing the wall-mounted embodiment ofthe invention.

FIG. 4 shows an illustrative arrangement of the fluid componentmonitoring and concentration maintenance system deployed in anon-recirculating bath configuration.

FIG. 5 shows the Wet Chemistry Module with respective fluid lines.

FIG. 6 depicts the Sign-On Screen that appears when the fluid componentmonitoring and concentration maintenance system is turned on or afterreset.

FIG. 7 depicts the Setup Screen 1, Analyzer Sequencer/Methods for thefluid component monitoring and concentration maintenance system.

FIG. 8 depicts a typical sequence section showing the use of theconditional IF, for the fluid component monitoring and concentrationmaintenance system.

FIG. 9 shows the Setup Screen 2, Analog Outputs and Relay Set Points,for the fluid component monitoring and concentration maintenance system.

FIG. 10 shows the Setup Screen 3, Calibration Data/Trigger, for thefluid component monitoring and concentration maintenance system.

FIG. 11 shows the Setup Screen 4, Analysis Timing, for the fluidcomponent monitoring and concentration maintenance system.

FIG. 12 shows a screen representative of Setup Screens 5 and 7, EndpointParameters, for the fluid component monitoring and concentrationmaintenance system.

FIG. 13 shows a screen representative of Setup Screens 6 and 8, AnalysisControl, for the fluid component monitoring and concentrationmaintenance system.

FIG. 14 shows a curve illustrating the values defined within the SetupScreens 5-8 of FIGS. 12 and 13.

FIG. 15 shows Service Screen 1, for the fluid component monitoring andconcentration maintenance system.

FIG. 16 shows Service Screen 2, for the fluid component monitoring andconcentration maintenance system.

FIG. 17 shows the first Data Screen, for the fluid component monitoringand concentration maintenance system.

FIG. 18 shows the second Data Screen, for the fluid component monitoringand concentration maintenance system.

FIG. 19 shows the Run Screen, for the fluid component monitoring andconcentration maintenance system.

FIG. 20 shows a screen appearing after the analyzer has started itsanalysis sequence, indicating the current step (“S1”) in the analysissequence underneath the time.

FIG. 21 shows a screen appearing once the analysis is completed,identifying a water concentration, as a number of milliliters of titrantrequired to reach the endpoint.

FIG. 22 shows a real-time analysis curve 1, displaying a rapid change insensor mV suggesting a lack of sample.

FIG. 23 shows a real-time analysis curve 2, exhibiting a “flat” sensorresponse whose cause, if the sensor mV is in an unexpected range, mayindicate a faulty sensor, connection, pre-amp or other electronic fault,or, if the sensor mV remain in the normal pre-endpoint range, mayindicate that reagent is not reaching the reaction vessel.

FIG. 24 shows a real-time analysis curve 3, reflecting a scenario thatusually occurs when the endpoint interpretation parameters have beenchanged within the Setup Screens, but the chemistry remains the same,indicating that the Setup parameters should be carefully reviewed, orthat a sensor that has drifted out of the normal endpoint window andshould be cleaned or replaced as necessary.

FIG. 25 shows a Run Screen appearing after an analysis is completed,displaying an [OPTIMIZE] menu option allowing for the optimization ofthe endpoint and the minimum and maximum increments used.

FIG. 26 shows an Optimize Screen, allowing the selection of the endpointwith the greatest gradient (strongest point of inflection), and thusoptimization of the endpoint and increments to invariably find thisendpoint.

FIG. 27 shows an apparatus for the generation of hydrogen peroxide andmonitoring of same, utilizing a Karl Fischer analysis tray.

FIG. 28 is a graph of titrant volume as a function of titration cyclesusing ceric ammonium sulfate, and showing the reproducibility of 2.5%peroxide determination.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

The present invention provides a multicomponent fluid monitoring andreplenishment system for measuring one or more components of themulticomponent fluid, e.g., a solvent mixture, and providing correlativequantitative feedback for on-line chemistry control, to facilitatereal-time correction of the composition and stable control of the fluidprocess.

Although described primarily and illustratively hereafter with referenceto semiconductor manufacturing removal of photoresist and post-etchresidue from semiconductor device structures by multicomponent solventmixtures including water and organic solvent(s) forming a semi-aqueoussolvent composition, the invention will be recognized as having broadapplicability to a wide variety of multicomponent fluid operations, inwhich it is essential to maintain the compositional character of themulticomponent fluid composition at a specific value or within aspecific range, in respect of the relative concentrations andproportions of components in the fluid composition. Thus, the inventionmay be employed in specific embodiments for monitoring andcompositionally controlling non-aqueous fluid compositions.

Accordingly, the ensuing discussion will be directed illustratively to asolvent monitoring and replenishment system according to the invention,which has been found to be particularly suitable for controlling solventprocesses such as photoresist and post-etch residue removal, in whichmaintenance of water concentration within specified limits is criticalto the proper operation of the process.

The illustrative solvent monitoring and replenishment system of theinvention in one embodiment thereof includes two primary components: (i)an analyzer unit, which monitors the concentration of the selectedsolvent mixture components using real-time methodology, e.g., aKarl-Fischer titration methodology, and (ii) a control unit whichfunctions as the process controller. The control unit compares theresults of the analyzer unit to pre-programmed specifications andcontrols the dispensing of one or more chemicals into the solventprocess system as required to maintain a desired component ratio ofsolvent components. The solvent mixture in one embodiment of theinvention is provided in one or more baths in the process system. Insuch case, the pre-programmed specifications preferably include volumeof each bath being monitored, frequency of monitoring and a titrationcalculation factor for calibration. The monitoring and controloperations are carried out in real time, i.e., the operations occurwithin a short period of time from the beginning of the monitoringprocess and there is no substantial time delay between the commencementof the sampling process and the control operation.

In one embodiment of the invention, the analyzer unit monitors theconcentration of the water component of a sample using a classic KarlFischer titration methodology. The analyzer unit in such embodimentincorporates a micro-size reaction vessel that requires as little as 5ml of KF titration solvent for each test. While the titration is carriedout in non-aqueous conditions, the KF solvent can contain trace amountsof water. In addition, water can originate from the methanol used to“shuttle” the sample as well as from the internal surface of theanalyzer's fluidics system. This problem is solved by a technique ofpre-titration of the solvents in the enclosed reaction vessel. These two“pre-dry” steps ensure maximum accuracy for the subsequent analysis.After titration solvent has been dried, a small amount of the sample(typically 1 ml) is extracted and its water content determined by KarlFischer titration using a dual-platinum sensor to detect the titrationend-point.

The process controller is used to accurately control the automaticreplenishment of the solvent components, in particular water,guaranteeing optimum and stable processing over an extended period oftime. Once the component analyzer determines the relative composition ofthe solvent system, the process controller can restore the system to thecorrect component ratio. Specific limits are pre-programmed into theprocess controller for the specific component(s) being targeted foranalysis. The results from the component analyzer are compared to thesespecification limits and, if determined to be below the minimumspecification value, amounts of the target component can be injectedinto the solvent solution to restore the required component ratio. Bymaintaining the component ratio of the solvent system withinpredetermined limits, the effective bath life of the solvent mixture canbe extended.

In many amine-based, alkaline solvent mixtures, such as the ST-26Ssolvent mixture commercially available from ATMI, Inc. (Danbury, Conn.),water constitutes an active and necessary ingredient for the functioningof the solvent mixture. When the water content is reduced below aparticular value, it renders the solvent incapable of performing thereactions required for photoresist and post-etch residue removal in thesemiconductor manufacturing removal operation for which the solvent isintended.

At an operating temperature of 60° C., the water content of such ST-26Ssolvent mixture decreases from an initial value of ˜16.5% to a finalvalue of ˜4.9% over 24 hours due to evaporation. When coupled to thesolvent monitoring and replenishment system of the invention, the samesolvent maintained a water content of ˜16.5% for over 24 hours. Bymaintaining a consistent water concentration in the solvent mixture, theperformance of the solvent will be stable over an extended period oftime. Maintaining chemical concentrations of the solvent components ofthe solvent mixture at predetermined set-point levels maximizes asolvent mixture's useful life and thus minimizes production downtime dueto re-pouring of solvents and re-qualification of those chemicalmixtures. In addition, more stable solvent mixtures yield a moreconsistent process performance, resulting in higher yield throughreduced failure rates.

The invention therefore provides in one embodiment a means and method ofin situ monitoring and H₂O injection of aqueous solvent mixtures usedfor the removal of bulk photoresists and post plasma etch/ash residues,which achieve an unexpected level of reduction, e.g., greater than 33%,and higher, of the overall consumption of semi-aqueous solvent cleaningsolution in such semiconductor manufacturing operation.

The system and method of the invention are usefully applied to themaintenance of semi-aqueous solvent mixtures that are employed for wafercleaning in semiconductor manufacturing applications. Approximately 75%of all of the solvents used for residue removal and photoresist“stripping” contain water. The recommended operating temperature forthese solutions is between 45-75° C., and the typical bath life forthese solutions is between 8-24 hours. The bath life is primarilydetermined by the loss of water due to evaporation. Using theconcentration analysis and solvent replenishment system of the inventionto analyze the solution and adjust the water level, the bath life can beincreased by at least 100%. This results in substantial savings in a)chemicals, b) downtime for chemical changes, and c) chemical disposalcosts. The invention thereby achieves a substantial advance in the artof cleaning semiconductor device structures.

Referring now to the drawings, FIG. 1 is a schematic representation of afluid component monitoring and concentration maintenance system 10according to one embodiment of the invention. FIG. 2B, described morefully hereinafter, is a schematic representation of the same system asmounted within a single cabinet, as a unitary system assembly, whereinthe cabinet is fabricated of a chemically-resistant material, e.g.,stainless steel, Teflon® polytetrafluoroethylene, or polypropylene.

The fluid component monitoring and concentration maintenance system 10includes an Analytical Information Module 12. The Analytical InformationModule includes the user interface, display, analysis control and datainput/output functions for the system, and functions as theconcentration analysis and controller unit of the apparatus. TheAnalytical Information Module also includes a Wet Chemistry Module 14 asthe solvent replenishment unit of the apparatus.

The Analytical Information Module is mounted in a separate enclosurefrom the Wet Chemistry Module in the embodiment illustrated in FIG. 1.The Analytical Information Module is provided with external connectorsfor coupling the Analytical Information Module 12 to the Wet ChemistryModule 14, via an interface cable harness 16. User-accessibleinput/output terminals (not shown in FIG. 1) are provided at the upperportion of the Analytical Information Module 12, under an access hatchon top of the housing of such Analytical Information Module. TheAnalytical Information Module is most advantageously mounted above or tothe side of the Wet Chemistry Module in the semiconductor manufacturingfacility.

The Wet Chemistry Module 14 of the apparatus is constructed and arrangedto perform highly accurate measurements and comprises:

a sampling system;

sensor(s);

a reaction vessel with mixer; and

a reagent dispensing system,

each of which is described more fully below.

Sampling System

During analysis, the apparatus captures a small quantity of sample froma by-pass loop connected to the process stream of the semiconductormanufacturing operation. The process stream comprises the cleaningsolvent mixture that is used to remove unwanted material from a waferstructure, e.g., a semiconductor device or semiconductor deviceprecursor structure on which material has been deposited, or isotherwise present.

Once isolated, the solvent mixture sample is transferred to the reactionvessel using a suitable solvent. After sample has been transferred tothe reaction vessel and analyzed, the reaction vessel is rinsed withsolvent to minimize the analyzer's exposure to aggressive processchemistry that may alter or otherwise adversely affect its operation inprolonged exposure.

The materials of construction of the sample system are appropriatelyselected for optimal use in a clean-room environment. The sample systemis designed to ensure reliable isolation between the process and thefluid component monitoring and concentration maintenance system, so asto minimize the possibility of process contamination. The sample systemdrain 18 (see FIG. 1) is most advantageously located below the reactionvessel.

Sensors

One or more sensors is/are used by the fluid component monitoring andconcentration maintenance system to plot each analysis curve, or fordirect measurement of the sample.

Reaction Vessel

The micro-volume reaction vessel of the fluid component monitoring andconcentration maintenance system is constructed of a suitablesolvent-resistant material of construction. A preferred material of suchtype is TPX engineering plastic, which is transparent yet remains highlyresistant to a wide variety of solvents.

The reaction vessel in one embodiment of the invention includes anintegral mixing system, comprising a solid-state magnetic stirrer andTeflon-coated stir bar, plus ports for up to two standard 12 mm pH,oxidation-reduction potential (ORP) or ion selective electrodes. Thereaction vessel in such embodiment also accommodates dual-platinumelectrodes for following the Karl Fischer reaction. This reaction vesselis sized and arranged to accommodate one transfer solvent and up tothree further analytical reagents (e.g. titrant, cleaning solvent,etc.).

Reagent Dispensing System

The fluid component monitoring and concentration maintenance systemcomprises a reagent dispensing system that in the illustrativeembodiment includes precision glass burettes, with digital linearactuator control, to provide a highly accurate reagent dispensingcapability. Each burette in such embodiment has a capacity of 5ml/stroke, gives a resolution of 0.01 ml, and is capable of theoreticalaccuracy of ±0.0015 ml.

In view of the deficiency of conventional syringe-pumps as susceptibleto damage caused by reagent leakage, the fluid component monitoring andconcentration maintenance system in the reagent dispensing system usesan “inverted burette” design. Each burette incorporates asolvent-resistant O-ring seal, e.g., a Kalrez® O-ring seal providing anoperational life of at least 3 months.

The fluid component monitoring and concentration maintenance system inone embodiment is designed for double containment of both the analyzerand the reagents, accommodating the sample inlet/outlet lines, thereagent lines, and the drain lines. The compressed air supply in sucharrangement is not double contained. The reagent enclosure also affordsdouble containment of the reagent lines.

The fluid component monitoring and concentration maintenance system ispreferably provided in a modular form to give a greater degree offlexibility in locating the apparatus in the semiconductor manufacturingfacility. For example, the Wet Chemistry Module, Analytical InformationModule and reagents can be located inside the associated process tool,in a service chase adjacent to the process, or in the sub-fab area ofthe semiconductor manufacturing plant, as may be necessary or desirablein a given application of the present invention. Preferably, the WetChemistry Module is located near the tool's pumps, piping and drain, andthe Analytical Information Module is mounted in a convenient andaccessible location either above or next to the Wet Chemistry Module.

Installation of the fluid component monitoring and concentrationmaintenance system can be effected on either a recirculatingbath/process or a non-recirculating bath/process, as described morefully hereinafter.

The fluid component monitoring and concentration maintenance system mayoptionally include a parallel display unit providing the same functionsas the Analytical Information Module, which is remotely mountable fromthe Analytical Information Module and the Wet Chemistry Module in thesemiconductor manufacturing facility, such as at a convenient locationin the cleanroom. This arrangement allows for a display unit of theAnalytic Information System to be positioned at its point of use in thesemiconductor manufacturing facility, e.g., for servicing andtroubleshooting the analyzer, while the remotely situated paralleldisplay unit allows the operator to manipulate the AnalyticalInformation Module from inside a cleanroom.

As an alternative to the use of double containment for reagents, thefluid component monitoring and concentration maintenance system mayinclude a reagent enclosure designed to contain an excess of the volumeof all possible reagents, e.g., the reagent enclosure may be sized andarranged to accommodate 110% of all possible reagents. Such reagentenclosure is fabricated of any suitable chemically compatiblematerial(s) of construction.

The reagent enclosure (if provided) can be mounted below the WetChemistry Module. The reagent enclosure can also be mounted to the leftor right of the Wet Chemistry Module, but it desirably is not mountedabove the Wet Chemistry Module, so as to eliminate the possibility of asiphon effect. When mounting the reagent enclosure, sufficient clearanceshould be maintained between the Wet Chemistry Module and the reagentenclosure, in order to access the Wet Chemistry Module drain and valve.

The fluid component monitoring and concentration maintenance system 10is shown in FIG. 2A as wall-mounted on wall 20 in a semiconductormanufacturing facility, utilizing “UNI-STRUT” or other wall mountingbrackets 22, 24, 26 and 28. As mentioned hereinabove, the fluidcomponent monitoring and concentration maintenance system 10 may also beintegrated into a process tool when the process tool contains sufficientspace for such integrated deployment of the fluid component monitoringand concentration maintenance system.

The fluid component monitoring and concentration maintenance system 10as shown in FIG. 2A includes a sample system, sensor(s) and mixedreaction vessel in the upper housing 30 of the Wet Chemistry Module 14.The upper housing as shown is coupled with a compressed air line 32, asampling system including sample #1 inlet/return 34, and sample #2inlet/return 36, drain 38, and exhaust port 48. The double containmentreagents line 40 interconnects the upper housing 30 with the lowerhousing 42 containing reagent supply means (not shown). The lowerhousing 42 is provided with an enclosure drain 18A, and exhaust 46.

Mounted on brackets 26 and 28 adjacent to the Wet Chemistry Module 14 isthe Analytical Information Module 12 including computational means, suchas a programmable general purpose electronic computer, microprocessor,central processor unit (CPU), or other suitable means, coupled todisplay 50 for visual observation of the output of the Module 14. TheAnalytical Information Module 14 is equipped with a power cord 44, forplug-in to a plug receptacle of an electrical power system, for poweringof the computational means and other means disposed in the housing ofthe Analytical Information Module 14.

The fluid component monitoring and concentration maintenance system 10is preferably arranged to sample the process solvent mixture from a bath68 in tank 66, equipped with a recirculating pump 72, as is shown forexample in FIG. 3. In such recirculating bath arrangement, a proportionof the sample is bled from the recirculation system in sample feed line80 and fed by feed/return line 56 to the fluid component monitoring andconcentration maintenance system 10. The sample enters the sample panelof the fluid component monitoring and concentration maintenance system10, passes briefly through its 3/2-way sample valve, and then returns tothe process tool 58.

The process tool 58 is disposed in relation to wall 60 demarcating aboundary between cleanroom 62 and service chase 64, as illustrated. Thetank 66 containing bath 68 is coupled with a fluid feed line 70 to thepump 72, from which the fluid is flowed in discharge line 74 thoughfilter 76 to recirculation line 78 for return to the bath 68.

Sampled fluid is returned from fluid component monitoring andconcentration maintenance system 10 in feed/return line 56 from return36, and passes in sample return line 82 to join with the fluidrecirculated in recirculation line 78 for return to the bath 68. Aportion of the fluid from the bath in recirculation line 78 is divertedin sample feed line 82 to the feed/return line 56 from which it flows inthe branched portion thereof to feed inlet 34.

The drains 38 and 18 from the Wet Chemistry Module 14 convergently joinin drain line 54, which is connected in turn to floor drain 57. Theexhausts of the upper and lower housings 30 and 42 are coupled in closedflow communication with the exhaust conduit 52, for fluid discharge ofexhaust from the system.

This “fast loop” concept minimizes chemical wastage and the possibilityof process contamination, and lessens the criticality of the distancebetween process and the fluid component monitoring and concentrationmaintenance system, as a consequence of the zero dead-volume of the fastloop arrangement.

FIG. 2B is a schematic representation of a fluid component monitoringand concentration maintenance system 11 according to a second embodimentof the invention utilizing a single, self-contained cabinet 13 formounting the system, in which the cabinet optionally may be equippedwith wheels 25 to facilitate relocation as a mobile system within asemiconductor manufacturing facility or alternatively the cabinet may befabricated without wheels to provide a semi-permanent installed systemthat is fixedly positioned in the semiconductor manufacturing facility.

FIG. 2B shows the fluid component monitoring and concentrationmaintenance system 11 in respective left-hand side elevation, frontelevation and right-hand side elevation views, as viewed from left toright in the drawing figure.

The left-hand side elevation view shows the unitary cabinet 13 asincluding an upper housing member 31 that is arranged to be swingablyopenable and closeable by means of the damped strut connector 33. Theupper portion of the housing includes a slidable tray 27 on which isprovided a display 29 which may comprise a monitor that is coupled witha keyboard and CPU mounted on the tray, for access to the programmableAnalytical Information Module embodied in the upper portion of thecabinet assembly.

The left-hand side elevation view of the unitary cabinet 13 as includinga clean dry air (CDA) port 15, a sample #1 inlet and return port 17, asample #2 inlet and return port 19, and enclosure drains 21 and 23. Thewheels 25 are of any suitable type, e.g., castor or roller types, andenable to system to be portably relocated in the semiconductorprocessing facility. In lieu of providing the system shown in FIG. 2B asa mobile assembly, the system may be deployed without wheels, toconstitute a stationary unit that is fixed positioned in thesemiconductor manufacturing facility.

The front elevation view of the system 11 shown in the central view ofFIG. 2B shows the cabinet doors 35 and 37 that permit access to thecomponentry of the Wet Chemistry Module.

The right-hand side elevation view shown in the right-hand portion ofFIG. 2B depicts the unit in a mirror-image relationship to the view ofthe system unit illustrated in the left-hand portion of the FIG. 2Bdrawing, and shows the exhaust ports 41 and 43 of the Wet ChemistryModule.

FIG. 3 shows an illustrative arrangement of the fluid componentmonitoring and concentration maintenance system 10 with a fast looprecirculating bath arrangement. The fluid component monitoring andconcentration maintenance system 10 as discussed is located in a servicechase adjacent to the process tool, and all fluid lines are doublecontained, with a fluid drain free-flowing with zero back-pressure. Flowof fluid through the recirculation fast loop depends on there beingsufficient pressure drop across the loop, which may necessitaterestriction or adjustment of the flow through the main recirculationsystem, as appropriate.

Alternatively, the fluid component monitoring and concentrationmaintenance system 10 may be deployed in a non-recirculating bathconfiguration, as shown in FIG. 4, wherein all parts and components arelabeled for consistency and ease of description, correspondingly as inFIG. 3. In this arrangement, sampling from the non-recirculating bath 68in tank 66 involves sample being withdrawn from the top of the bath by asampling pump 72, e.g., a pneumatic diaphragm-type pump, for flow offluid from the bath 68 to pump feed line 70, and from pump 72 in samplefeed line 80 to the feed/return line 56 from which it flows in thebranched portion thereof to feed inlet 34. The sample return fluid flowsfrom system 10 in feed/return line 56 from return 36, and passes insample return line 82 to the bath 68.

In the non-recirculating bath configuration, the fluid componentmonitoring and concentration maintenance system 10 can be located in thefab or in an adjacent service chase. There is a greater possibility ofentraining air in the sampling line in the non-recirculating bathconfiguration than in the recirculating bath mode, particularly when thebath is being drained. It therefore is preferred to locate the tip ofthe sample extraction pipe as close as possible to the bottom of thebath in the non-recirculating bath configuration.

The fluid component monitoring and concentration maintenance system 10preferably is provided with suitable valving (not shown) to allow thefluid component monitoring and concentration maintenance system to beisolated from the associated process using the solvent mixture beingmonitored by the apparatus. Such valving may include automatic “failclosed” isolation valves, which close if there is an interlockviolation. Corresponding valves or check-valves preferably are mountedin the sample return lines to eliminate the chance of back-flow from theprocess in the event of a leak.

The Wet Chemistry Module includes four 5 ml burette glasses mounted onburette guide-posts. Tubing connects the respective reagent bottles withthe burette glasses in the Wet Chemistry Module.

FIG. 5 shows the Wet Chemistry Module 14 with the respective fluidlines, including compressed air line 32, a sampling system includingsample #1 inlet/return 34, and sample #2 inlet/return 36, and drain 38.The reagent lines are fed through double containment tubing of reagentsline 40 to the reagent enclosure. An air source (of clean dry air (CDA))is connected outside the Wet Chemistry Module by an appropriatecoupling, e.g., a ¼″ OD Flare-tek™ fitting on line 32. The sample(s)inlet 34 and return 36 are connected at the sample valves by appropriatecouplings, which may also comprise ¼″ OD Flare-tek™ fittings. The drain38 is connected to the reaction vessel, and may for example comprise3×⅛″ tubes.

The fluid component monitoring and concentration maintenance system 10in one embodiment is constructed and arranged to monitor theconcentration of water in a conventional n-methyl pyrrolidone(NMP)-based photoresist stripping solvent. The apparatus may beconfigured to allow multiple, e.g., two or more, process streams to beindependently analyzed.

The water content of the sample is measured by a suitable analyticaltechnique, e.g., Karl Fischer titration, following an analyzer pre-dryphase, in which the endpoint is detected using a double-platinumelectrode pair driven by a constant current module.

The fluid component monitoring and concentration maintenance system 10may thus be arranged to perform a water in NMP analysis to determinesample water content by classical Karl Fischer titration technique,performed in non-aqueous conditions. The titration reaction requiresthree components: sulfur dioxide, iodine and water. The sulfur dioxideis readily oxidized with iodine—but only in the presence of water. Asimple representation of the chemistry isSO₂+I₂+2H₂O=H₂SO₄+2HI.

The sulfur dioxide and iodine, along with supporting solvents, arecombined in commercially available Karl Fischer titrant/solvent packagessuch as those commercially available under the Hydranal trademark.

In the sample titration, the sample is titrated against the Karl Fischertitrant until any water contained in the sample has been completelyconsumed. Once all the water has been removed, a sharp endpoint isdetected using a polarized (constant current) double-platinum electrode.

The detection of the endpoint in the Karl Fischer titration isaccomplished by amperometric detection. Amperometry relies on themeasurement of an electric current flowing between two polarizedelectrodes. The current flow is controlled by reactions taking place atthe electrodes (not by the conductivity of the solution). Theseelectrode reactions are:at the cathode I₂+2e→2I⁻, andat the anode 2I⁻−2e→I₂.

Before the endpoint of the titration, there is enough iodide presentfrom the reaction of the Karl Fischer reagent with the sample water, sothat there is no obstacle for the anode indicator reaction to proceed.However, no iodine is available for the cathode reaction, and thisabsence limits current flow between the electrodes. Only at and afterthe endpoint are iodine and iodide both present. Current then flows andthe potential between the polarized indicator electrode drops to give anexceptionally sharp endpoint signal.

A very small (few micro-amp) current is imposed between the two platinumindicator electrodes. The fluid component monitoring and concentrationmaintenance system optionally may be provided with an integralconstant-current supply, which powers the platinum indicator electrodes.

The Karl Fischer titration is carried out under “non-aqueous”conditions, but in a typical two-component Karl Fischer reagent set, thesolvent usually contains considerable amounts of water. Further watercontamination can come from the internal surfaces of the analyzer'sfluidics system that come into contact with the sample, as well as watercontamination deriving from atmospheric moisture.

The problem of obtaining a state of system dryness is solved in thefluid component monitoring and concentration maintenance system of theinvention by a technique of pre-titration of the Karl Fischer solvent,plus the use of completely enclosed titration equipment with minimalunfilled volume. Thus the solvent used to transfer the sample to thetitration vessel is first dried in a pre-titration step, using the KarlFischer titrant itself. This dried solvent can then be used to flush outthe sample transfer lines again prior to the sample capture step, whereit again can pick up water necessitating a further pre-titration todryness. Usually only two such “shuttle” drying steps are required, butit will be recognized that greater or lesser numbers of drying steps maybe necessary or desirable in a given application of the invention.

In the assembly of burettes provided in the fluid component monitoringand concentration maintenance system of the invention, the role of eachburette is as follows:

Burette 1- Karl Fischer solvent K (solvent for water determination inketones);

Burette 2- methanol (optional flushing agent); and

Burette 3- Karl Fischer titrant K, 5 mg/ml (titrant for waterdetermination in ketones).

The burettes are primed with reagent in a flushing procedure, carriedout by the following sequence of steps:

-   -   Step 1. Power up the analyzer.    -   Step 2. Have each of the reagents ready in appropriate reagent        bottles (e.g., the original chemical manufacturer's bottles).    -   Step 3. Unravel the burette inlet lines. Take a first reagent        line (reagent line #1) and feed it through the reagent bottle        cap, and slip the end of the tube over a tube weight barb.    -   Step 4. Drop the end of the tube, with its tube weight, into the        selected reagent bottle, and secure the cap.    -   Step 5. Repeat the above Steps 1-4 for the second and third        reagent lines (reagent lines #2 and 3).    -   Step 6. From the Sign-on Screen of the Analytical Information        Module (described hereinafter in greater detail), press        [SERVICE], then [NEXT]. Press [ENTER], and the number after        “Flush Burette” will be underlined by a flashing cursor.    -   Step 7. Using the [UP] or [DOWN] keys, select the number of the        burette desired to be flushed, then press [ENTER].

Following such steps, the burette will begin a standard flushingroutine; the burette's piston will cycle up and down three times, duringwhich any air and excess reagent will be expelled into the reactionvessel. At the end of the cycle, the burette should be full. If not, theroutine is performed again, and the procedure is repeated for the otherburettes until each is completely flushed. It is to be appreciated thatKarl Fischer K reagents are unusually viscous, and may requireadditional flushing.

The Analytical Information Module is programmatically arranged withsoftware in a computational unit for operating the system. The computercontrolled fluid component monitoring and concentration maintenancesystem will now be described with reference to the software operation,and appertaining screen displays.

The Setup Screens displayed on the visual output display of theAnalytical Information Module contain parameters that the fluidcomponent monitoring and concentration maintenance system will use inits operation. These parameters allow the fluid component monitoring andconcentration maintenance system to run a specific analysis sequence,find the endpoint(s), calculate and report the results.

The Calibration Screens are live read-outs of the electrode signals.Although the Karl Fischer electrode pair does not require routinecalibration, these screens are still useful for troubleshooting theelectronics and the chemistry.

The Service Screens allow manipulation of the system. Service Screen 1allows the operator to force open any valve or relay. Service Screen 2allows the operator to flush the burettes, set the analog outputs, andperform additional troubleshooting operations. The Data Screens allowthe operator to review the stored analysis data. This data can bedisplayed either numerically or graphically. The Data Screen also allowsthe operator to download the data to a host computer for import into aspreadsheet program. The Run Screen allows the operator to place theAnalytical Information Module into a single run or multiple runsoperation. This screen is displayed at all times during analysis.

The various screens associated with the operation of the fluid componentmonitoring and concentration maintenance system will now be described,as associated with an illustrative embodiment of the invention.

The Sign-On Screen is shown in FIG. 6, and is the first screen to appearwhen the fluid component monitoring and concentration maintenance systemis turned on or after reset. From this screen all the features of theoperating software can be accessed.

The fluid component monitoring and concentration maintenance system inone embodiment is operated through “softkeys.” Data also is enterable bythe softkeys. The operation of the fluid component monitoring andconcentration maintenance system is simplified by having a minimumnumber of keys. In the preferred arrangement of the system, only thekeys needed to perform a function for the displayed screen are active.

Many modes accessible from the Sign-on Screen are actually made up ofseveral screens linked together. The “softkeys” are, however, alwaysclearly labeled and allow an unambiguous and simple use of the manyfunctions available.

The fluid component monitoring and concentration maintenance systempreferably is passcode-protected, whereby all parameters can beprotected from unauthorized programming. The passcode entry routine isinitiated by pressing the [SETUP] key for at least 2 seconds, andentering the passcode as instructed in the prompt line.

The fluid component monitoring and concentration maintenance system isarranged in one embodiment so that the first time the apparatus isconnected to a main power source, the passcode “111111” is announced,and opportunity is afforded to customize the passcode. Any passcodeother than the original “111111” will not be displayed, therefore thepasscode remains a secret. If the programming mode has not been enteredwith the passcode, viewing of all screens is still possible, but thecursor and the keys [UP], [DOWN], and [ENTER] which are necessary forprogramming the fluid component monitoring and concentration maintenancesystem do not appear.

The programming mode is cancelled in the Sign-on Screen when any buttonis pressed for more than two seconds.

In the programming mode, the [SETUP] key has a double function. A shortpress transfers the operator to the screen for inspection of the dataonly. No programming is allowed. If, however, the [SETUP] key is pressedfor longer than two seconds, the passcode input routine is accessed. Onsuccessful input of the passcode, full programming is possible in thefluid component monitoring and concentration maintenance system SetupScreens.

In such embodiment, the programming can be carried out by individualparameters or by loading the default values. The default values areloaded by pressing [CONTINUE] for longer than two seconds. Otherwise,the data values remain intact until programmed to another valueindividually.

If a reset occurs during the RUN mode, upon restarting, the fluidcomponent monitoring and concentration maintenance system will return tothe Sign-on Screen and remain idle until further instructions are given.The Analytical Information Module cannot be placed into any mode untilthe cause of the reset is corrected (such as an open door).

The ensuing discussion is directed to programming of the AnalyticalInformation Module of the fluid component monitoring and concentrationmaintenance system.

In the programming mode, the [UP] or [DOWN] keys are used to move to theline required. The [ENTER] key is depressed, and the [UP] or [DOWN] keysare utilized to change the currently selected units. Pressing [ENTER]accepts the currently indicated data and moves the cursor to the nextdata field for input of that information. This process is repeated untilall the data are entered. The cursor will return to the beginning of theline where the following steps are possible:

Re-entering the data by selecting this parameter with [ENTER],

Moving the cursor with [UP] or [DOWN] to another parameter on thescreen,

Returning to the Sign-on Screen with [MAIN], and

Accessing the next Setup Screen with [NEXT].

Concerning the sequence parameters, all times preferably are in decimalminutes (e.g., 0.3 minute (=18 seconds)), all volumes are inmilliliters, and the burettes are numbered 1-4 from left to right.

The Setup Screen 1, Analyzer Sequencer/Methods, is shown in FIG. 7. Theanalyzer sequencer/methods screens allow the analysis routine to bedefined. The FIG. 7 screen shows a routine that allows the fluidcomponent monitoring and concentration maintenance system to take asample (for 0.3 minute, or 18 seconds), titrate the sample with titrantfrom burette 2, empty the reaction vessel, and lastly re-fill thereaction vessel with methanol from burette 1.

In one embodiment, the Setup Screen 1 offers up to 32 steps, allowingcustomization of the function of the fluid component monitoring andconcentration maintenance system. The available commands are:

MS—Measure and Set

-   -   Not required in the Water-in-NMP application.

BUR—Burette

-   -   Causes the selected burette to “draw back” a specified amount of        reagent from the burette's tip. This feature is useful for        eliminating the possibility of reagent leakage contaminating a        particular step in the analysis sequence. The syntax is:        -   BUR        -   burette#        -   volume

M1-M5—MACRO command

The MACRO commands, M1 through M5, allow custom valve sequences to beintroduced into the analysis scheme.

IF, FI—Logical branch

The conditional IF command allows a section of the programmed sequenceto be performed only when the given condition is satisfied. The sectionsubject to the IF condition is defined between the IF command and the FIcommand. The syntax is:

-   -   IF    -   Condition    -   Value

The available tests are:

-   -   pH>, pH<, mV>, mV< . . . Tests based on sensor output    -   ml>, ml< . . . Tests based on endpoint volume    -   x . . . A test based on number of elapsed cycles    -   Q2>, Q2< . . . Tests based on the signal being fed into the        specified level sensor (useful for remote stream or method        selection).

A typical sequence section showing the use of IF . . . FI is shown inFIG. 8

In this example, the IF branch will be carried out only when theprevious titre was less than 0.50 mL. In this case, the titration willbe repeated using burette 2 (where presumably a more dilute reagent isstored). The titrate command in the IF loop is assigned the R tag toindicate that it is not a determination on a new sample but a repeat ofthe previous. The second data field indicates the degree of dilution orconcentration of the reagent over that used for the first titration.

A Ramp (RMP) command may be employed to automate validation experimentscommon during analyzer startup and method development. The RMP commandfunctions like a C command, but adds reagent (usually a standard orsample) from the specified burette to the reaction vessel in amountsthat increase by the specified volume with each cycle. The syntax is:

-   -   RMP    -   burette#    -   volume increment

When the RMP command is used, a complete set of titration curve data isautomatically outputted via the RS232 interface after each analysis.

The Blow (BLO) command is used as an “accelerated vessel empty” commandto initiate use of CDA to blow the contents of the reaction vessel tothe drain. The syntax is:

-   -   BLO    -   Time

The Shuttle (STL) command follows the Td command, manipulating theburette 1 to withdraw up to 5 mL of the reaction vessel's contents andthen force it back into the titration vessel again. After the shuttlingis completed, a further “polish” dry-down of the solvent isautomatically performed. This sequence is designed to ensure athoroughly dried sampling and analysis system prior to introduction ofthe sample. The syntax is:

-   -   STL    -   burette#    -   volume

The Else branch (ELS) command is used with an IF . . . FI loop; when theIF condition is not met, then whatever follows the ELS command isperformed.

The S1w or S2w commands (Sample from stream 1 or stream 2 prior to KarlFischer (water) titration) trigger the preprogrammed sampling sequencein preparation for titration of water in the sample. The time is thatallowed for purging the sample loop. The syntax is:

-   -   S1w    -   Time

The Tw1 (Titrate water using method 1) command calls for the titrationof water in the sample, using the “method 1” parameters. The titrationparameters are defined in column “B3 H2O 1” in Setup Screens 5 and 6.

The Tw2 (Titrate water using method 2) command calls for the titrationof water in the sample, using the “method 2” parameters. The titrationparameters are defined in column “B3 H2O 2” in Setup Screens 7 and 8.

The Td (Titrate to dryness) command dries the Karl Fischer solvent priorto capturing the sample. This command typically precedes the STLcommand. The titration parameters are defined in column “B3 dry” inSetup Screens 7 and 8.

The C1-C4 (Condition with reagent 1-4) command calls for a definedvolume of reagent to be dispensed into the reaction vessel from thespecified burette. The syntax is:

-   -   C1    -   volume

The W (Wait) command causes the analyzer to pause at this point for thedefined length of time. This command is typically used to allow a sensorto stabilize prior to beginning a titration. The stirrer operatesthroughout this time. The syntax is:

-   -   W    -   Time

Setup Screen 2, Analog Outputs and Relay Set Points, is shown in FIG. 9.In Setup Screen 2 the analog outputs and the relay functions are set.

The fluid component monitoring and concentration maintenance system hasup to four analog outputs. The analog outputs are standard 4 . . . 20 mAconfiguration. The assignment of the outputs is given in the text inputin the left data field. An output value of 4 mA always represents aresult (concentration) of zero. The concentration corresponding to theend of the range may be programmed freely, within the constraints of theinput data format: 0.01 to 9999.99 in the right data field. Forinstance, if a typical concentration is usually around 6%, the analogoutputs can be advantageously set to be 0 to 10%, so that the normaloperating range is in the middle of the analog output range.

In the Relay Assignments, the four/six alarm relays can be assigned thefollowing functions:

-   -   1>, 1<, 2<, 2>. . . relay closes if specified result is less        than or greater than the specified value    -   err . . . relay closes if any error condition is detected    -   off . . . relay is disabled    -   Q2, Q3, Q4 . . . relay closes if the specified level sensor is        activated

The above assignments are made in the first field of the relay set upline. The sample concentration that triggers an alarm is set in the datafields to the right. The data is in decimal format. If a relay has beenassigned to a level sensor, then the concentration data field isirrelevant.

The Setup Screen 3, Calibration Data/Trigger, is shown in FIG. 10. ThisSetup Screen allows for process or factor calibration data to beentered, which are used to convert the volume (ml) of titrant used toreach the endpoint into units of concentration (e.g. wt %).

The fluid component monitoring and concentration maintenance system canmanipulate the endpoint volume (or “titre”) in one of two ways:

-   -   in a first approach, the analyzer's “factor” is calculated from        first principles, taking into account sample size, reagent        concentration, reaction stoichiometry and required result units;        and    -   in a second approach of “process calibration,” the analyzer is        synchronized with a trusted laboratory analysis result.

The parameter “calibration type” is used to define whether thecalculation of the concentrations is conducted according to classicaltitration rules of balancing chemical equivalents (factor) or using aparameter that has been determined from a process calibration (process).

The analyzer's calculation factor can be derived from first principlesusing the following equation:Calculation Factor=(C _(tit) ×RR×U×MW)/V _(samp)

-   -   where: C_(tit)=Titrant Concentration (moles/liter)    -   RR=Reaction Ratio (moles of sample that will react with each        mole of titrant)    -   U=Unit factor (typical values: “1” for g/l, “0.1” for %, “1000”        for mg/l etc.)    -   MW=Molecular Weight of sample species (e.g. HF=20)    -   V_(samp)=Volume of sample taken (typically 0.25-1 ml)

Alternatively, a “process calibration” can be performed, whereby thefluid component monitoring and concentration maintenance system isadjusted to match results from a laboratory analysis. This procedure maybe required if the inflection point seeking algorithm is used, butlaboratory procedures takes an endpoint (somewhat displaced) from theinflection point of the titration curve.

Having entered the laboratory-determined concentration, the fluidcomponent monitoring and concentration maintenance system will calculatethe conversion factor that relates concentration to titre value, anddisplay that value. If no valid data is available, then an ERROR 32 willbe generated.

The Analyzer Trigger Mode determines what controls the analysis timing.If the fluid component monitoring and concentration maintenance systemis in LOCAL trigger mode, the analyzer will be operated through thekeypad and its own internal timer.

If the fluid component monitoring and concentration maintenance systemis in REMOTE trigger mode, the analyzer will await an external signalbefore beginning its analysis cycle. Typically, this signal would be arelay closure performed by an external programmable logic controller(PLC). After the analysis cycle is completed, the analyzer sends a readysignal as a handshake (via alarm relay). If the fluid componentmonitoring and concentration maintenance system is in COMPUTER triggermode, it is fully controlled via its integral RS232 interface.

The Setup Screen 4, Analysis Timing, is shown in FIG. 11. This screensets the parameters for the timing of the fluid component monitoring andconcentration maintenance system. Inputs for time, date, and analysisinterval are provided on this screen.

The Titre Frequency command sets the time interval between analysiscycles. Units are decimal minutes. If the titration actually takeslonger than the programmed interval, the next titration will commence 5seconds after the finish of the previous titration. In these 5 secondsthe operator may abort a sequenced titration by pressing the active[STOP] soft key. If the titre frequency is less than or equal to one(1), then the fluid component monitoring and concentration maintenancesystem will perform mathematical models in a demonstration mode. If thevalue is less than 0.3, then the burettes will be inactive. At the sametime the data bank will be loaded with computer generated data.

The Equilibration Time on the Setup Screen has a decisive effect on thespeed and accuracy of the titration. This is the time allowed for thesystem to come to equilibrium after the dispensing of titrant. Aftereach titrant addition, there will be a certain time required for thereagent to become perfectly mixed in the whole solution, then time forthe sensor to equilibrate to the new mV value. An equilibration time of6 seconds is typical for the Karl Fischer titration method.

The Data Smoothing entry on the Setup Screen takes cognizance of thefact that titration curves in non-aqueous solvent are sometimesextremely “noisy”. The Data Smoothing parameter allows the titrationcurve to be smoothed mathematically, improving the consistency ofanalysis results. This parameter typically varies from 0.1 to 10. TheWater-in-NMP application typically requires little smoothing, so thedefault value of 1 is generally adequate in such application.

The Setup Screens 5 and 7, Endpoint Parameters, are representativelyillustrated in FIG. 12. These Setup Screens determine the parametersthat will be used to define the shape of the analysis curve and how theendpoints are interpreted. The data fields are arranged in four columns(two on each screen) representing parameters for the four titrationprocedures:

-   -   B2 acid (burette 2, acid analysis)—these parameters are        associated with the “Ta” command    -   B3 H2O 1 (burette 3, water analysis 1)—these parameters are        associated with the “Tw1” command    -   B3 H2O 2 (burette 3, water analysis 2)—these parameters are        associated with the “Tw2” command    -   B3 dry (burette 3, pre-dry)—these parameters are associated with        the “Td” command

The End Point entry on this Setup Screen reflects the fact thatregardless of whether a fixed setpoint, seeking, or seek/set inflectionpoint algorithm is used, the expected endpoint value (usually expressedin mV) must be given. In each case this value is used to assign theendpoint/inflection points to a particular parameter being measured.

The Sensor entry is set to KF for Karl Fischer titration.

The Window/Smoothing entry defines the tolerance (either side of theEndpoint parameter) in which the seeking algorithm will search for theendpoint. Whenever the electrode signal resides in this window, thetitrant additions will be driven to their minimum allowable value.Although the algorithms to detect the endpoints are very robust,additional safety measures are provided by the Window/Smoothingcapability to unambiguously interpret the endpoint data and to assignthe appropriate results.

The “End” (Titre End) parameter defines the limit of the titrationexperiment; when this value is exceeded, the analysis will terminate.Using a fixed setpoint algorithm requires that the titre end be set ator shortly after the endpoint point. The self-seeking and seek/setinflection point algorithms, however, require that reagent be added tothe sample in excess such that a symmetrical curve is obtained on bothsides of the inflection point.

In respect of the Algorithm entry on the Setup Screen, three endpointpoint algorithms are available:

-   -   SEEK—titrate to an inflection point (“self-seeking”)    -   SETPOINT—titrate to a fixed setpoint value    -   SEEK/SET—titrate to an inflection point, then if failed to a        fixed setpoint value

The first algorithm is an advanced curve fitting routine that searchesfor the inflection point on the titration curve (“seeking” method).

The second algorithm is a “setpoint” method that finds the titre valuefor the position of the theoretical/preset end point programmed in theparameter list (i.e., the fluid component monitoring and concentrationmaintenance system titrates to a target electrode signal).

The third algorithm is a hybrid of the seeking and setpoint algorithms.In the event there is an insufficient number of points along thetitration curve for the seeking method, the fluid component monitoringand concentration maintenance system will automatically shift toset-point analysis.

The seeking method will find the true inflection point regardless of themV electrode drift (provided the drift stays within the defined endpointwindow). This means that the electrode does not have to be calibrated.On the other hand, the value of the titre may differ from resultsobtained using a fixed set point titration if the position of the setpoint does not exactly correspond with the position of the inflectionpoint on the analysis curve. For this reason the process calibrationfeature has been built into the fluid component monitoring andconcentration maintenance system to provide the option of using theadvanced inflection point seeking method, while allowing results to bescaled to match those obtained in a well calibrated laboratory setpointdetermination.

The Titration Direction entry on the Setup Screen indicates thedirection the sensor signal is expected to move as the analysisproceeds. If the sensor signal proceeds in the wrong direction, theanalysis is aborted and an error code is displayed on the liquid crystaldisplay (LCD) of the apparatus.

In addition to defining the expected sensor response, the Direction_1and _2 options allow further control of the titrant addition mode. Thiscan be particularly useful for titrations with very unpredictable andabrupt titration curve profiles. When using these modes, the expectedendpoint volume is entered in the corresponding “goal” field of SetupScreens 6 and 8.

Setup Screens 6 and 8, Analysis Control, are representatively shown inFIG. 13. The analysis control screens determine how titrant is added andhow the result is calculated/displayed.

Minimum and Maximum Increments (ml) entries are shown on therepresentative Setup Screen in FIG. 13. The minimum and maximum titreincrements have a large influence on the speed and accuracy of thetitration.

In principal, the smaller the minimum increment value the greater willbe the accuracy. A small minimum increment will, however, result in aslow titration, since many more points will be measured. A maximum ofmeasurement points is allowed per titration curve, to ensure that theminimum increment enables a complete curve will be taken with less than201 points.

The maximum value defines the upper speed of the titre when far from theendpoint point. Care should be taken with large values in case the firstfew additions of reagent shoot the curve past the endpoint point.

All fluid component monitoring and concentration maintenance systemtitration endpoint determination algorithms interpolate between datapoints, thereby giving resolutions that are higher than the minimumreagent dispense volume.

The Pretitre/Goal entry reflects the fact that if sample concentrationremains reasonably stable relative to the frequency of analysis, then itis likely that sequential analysis will yield similar endpoint volumes.Under these circumstances, it is possible to perform part of the nexttitration very rapidly by adding a proportion of the last titre in one“slug”, thus coming close to the end point almost instantaneously. Sucha “predose” will allow the titration to be performed with the maximumspeed without sacrificing accuracy.

The pretitre parameter can be set to any value between 0 and 1; “0”represents no predose at all (i.e. titration proceeds normally) while“1” represents adding 100% of the last endpoint. Typical pretitre valuesare in the 0.2-0.7 range, depending on how predictable and stable thesample concentration proves to be.

When the UP/DOWN_1 or UP/DOWN_2 addition modes are selected in SetupScreens 5 and 7, then the pretitre fields becomes “goal” fields; in thiscase, the expected endpoint volume in ml. Is entered.

The Calculation Formula is selected on the Setup Screen, and in the FIG.13 embodiment, is “normal.” The conversion of the titration endpointvolume to a concentration reading (see discussion herein concerningSetup Screen 3, Calculation Factors) can be performed in several ways.The most common and simple is the “normal” calculation, in which theendpoint volume is directly multiplied by the calculation factor.However, a number of alternative calculations are available that permitmore advanced titration techniques such as back titration to beexploited.

The Mix Correction entry on the Setup Screen is usually left at 0.00 forthe Water-in-NMP application.

Although the fluid component monitoring and concentration maintenancesystem is typically provided for use with the default parameterspre-loaded, so that the apparatus is suitable for running the analysisquickly and accurately from the initial operation of the operation ofthe apparatus, the apparatus nonetheless may require adjustment to thedefault values during the operational life of the apparatus, toaccommodate changes in process conditions, sensor response or new userrequirements.

The curve in FIG. 14 illustrates the values defined within theaforementioned Setup Screens 5-8. The endpoint is shown at 800 mV, but a100 mV tolerance has been established by the Window setting. Therefore,the fluid component monitoring and concentration maintenance system willlook between 700 and 900 mV for the point of inflection. The titre endis set at 1100 mV, allowing the curve to be drawn symmetrically, asrequired by the seeking algorithm. The maximum increments allow theanalysis to be speedy, but once the fluid component monitoring andconcentration maintenance system detects a change in the slope it willslow down the analysis to the minimum increment.

In the circled portion of the curve in the graph of FIG. 14, the datapoints are much closer together to give the fluid component monitoringand concentration maintenance system the best chance at finding the mostaccurate endpoint. This allows for a quick measurement, yet stillmaintains a high degree of accuracy.

The Service Screens 1 and 2 shown in FIGS. 15 and 16, respectively,allow testing of major functions of the fluid component monitoring andconcentration maintenance system hardware, including all of the outputs,dispensers, relays and valves, by manually actuating them. They alsoallow programming of Macros.

In Service Screen 1, any item can be actuated by simply scrolling thecursor down to the chosen item and pressing [ENTER]. The digit to theright of the item will change from 0 to 1, and the operator will be ableto observe the item actuating correctly.

Upon exiting the Service Screens, any actuated items will beautomatically deactivated.

Up to 16 valve/relay selected operations can be custom programmed tocreate a custom operation such as switching on external pumps orcustomizing sampling operations. Up to five macros can be saved in thememory of the fluid component monitoring and concentration maintenancesystem.

To program a Macro, the [MAIN/MAC] button is first pressed and held for10 seconds. Once in the Macro Screen, [START] is pressed and then thechosen valves were operated before [STOP] is pressed to save thesequence. When recalled, via the M command in Setup Screen 1, the Macrois repeated in exactly the same sequence (including timing).

Service Screen 2 (FIG. 16) features additional controls that flushing ofthe burettes, setting of the analog outputs etc.

The data screens of the fluid component monitoring and concentrationmaintenance system provide access to all of the stored data of theapparatus. The fluid component monitoring and concentration maintenancesystem stores up to 1400 measurements, with the most recent measurementreplacing the oldest measurement.

The first Data Screen in FIG. 17 shows the data in numeric form.Pressing [UP] or [DOWN] moves the data one place. If these buttons arepressed for longer than 3 seconds, the display moves up or down onewhole day to the first measurement of that day (first after midnight).Pressing [PRINT] will give access to the soft keys [RESULTS] or [CURVE].Pressing [RESULTS] briefly will download, via the RS232 output of theAnalytical Information Module, the data of the day currently shown inthe display. Pressing for longer than 3 seconds will download all thedata held in the memory. Pressing [CURVE] will download the lasttitration curve.

The second Data Screen in FIG. 18 shows the results in a graphicalformat, displayed in 24 hour blocks. To move between days the [BACK] and[FORWARD] softkeys are used. The [DISPLAY] key is used to move betweencomponents. The scale of the graph is determined by the analog outputsdefined in Setup Screen 2.

The graphical display feature enables a quick glance at the process overa short time period. For a higher resolution, the data is downloaded tobe imported into a spreadsheet. The downloading procedure using Windows95/98 operating system software is set out below.

-   -   In Windows, click on the “Start” button. Move to “Programs,”        select “Accessories,” and choose the “HyperTerminal” icon.    -   Click on the HyperTerminal icon.    -   Create a HyperTerminal icon, by giving the HyperTerminal        directory an appropriate name such as “SemiChem.” Now select an        icon for the new “SemiChem” directory.    -   When done, click “OK”.    -   The Phone Number Window will be displayed next. Verify which COM        port the RS232 cable is connected to on the computer. In most        cases this will be COM 2. To select COM 2, move the cursor until        “Direct to COM 2” is displayed. Click on “OK.”    -   The Port Setting Window will be displayed next. The following        setting must be selected:        -   Bits per second: 2400        -   Data bits: 8        -   Parity: none        -   Stop Bits: 1        -   Flow Control: Hardware    -   When this is done click “OK.”    -   The apparatus is now ready to download data. From the        HyperTerminal window click on the icon just created.    -   Next select “Transfer” from the menu bar. The Capture Text        Window should now be displayed, and it should read:        Folder C:\Program Files\Accessories\Hyperterminal\Capture.txt    -   At this time rename the file with an appropriate name followed        by the .txt extension.        -   On the Analytical Information Module, press the [DATA]            softkey        -   On the Analytical Information Module, press the [PRINT]            softkey        -   On the Analytical Information Module, press the [RESULTS]            softkey for the analysis data, and press [CURVE] softkey for            the most recent electrode response data.        -   The data from the fluid component monitoring and            concentration maintenance system will be sent to the            computer and displayed on the computer screen.        -   Once the Text Capture has stopped, the data can be imported            into any spreadsheet program (as comma delimited text).

The following Setup Screens are typical of parameters suitable foranalysis of water in NMP-type photoresist stripping solvent. In thisexample, solvent is analyzed only on stream 1, the sample size is 0.5 mland the expected sample composition is 2 wt % water in NMP. Setup Screen1 BLO C1 Td STL W S1w Tw1 BLO W BLO C2 0.50 5.00 1 0.30 0.40 0.40 0.200.20 5.00 3.00 Setup Screen 2 Output 1 = Conc.1 Max . . . 2 Output 2 =Conc.2 Max . . . 2 Output 3 = Conc.3 Max . . . 2 Output 4 = Conc.4 Max .. . 2 Relays 1-6 = off Setup Screen 3 Calibration Type = FactorCalculation Factor 1 = 1.000 Calculation Factor 2 = 1.000 CalculationFactor 3 = 1.000 Calculation Factor 4 = 1.000 Analyzer Trigger = LocalSetup Screen 4 Titration Frequency (min.) = 30 Equilibration Time (sec.)= 6 Data smoothing = 1.00 Acid Cal = 4.00 Water Cal = 1.00 Setup Screen5 Endpoint (pH/mV) = — 200.00 Endpoint Window = — 10.00 Titre End = —190.00 Sensor = — KF Algorithm = — Setpoint Titrate up/down = — downSetup Screen 6 Min.Increment (ml) = — 0.01 Max.Increment (ml) = — 0.05Pre-titre/Goal = — 0.00 Calculation Formula = — Normal Units = — % MixCorr. = — 0.00 Setup Screen 7 Endpoint (pH/mV) = — 200.00 EndpointWindow = — 10.00 Titre End = — 190.00 Sensor = — KF Algorithm = —Setpoint Titrate up/down = — down Setup Screen 8 Min.Increment (ml) = —0.01 Max.Increment (ml) = — 0.03 Pre-titre/Goal = — 0.00 CalculationFormula = — Normal Units = — % Mix Corr. = — 0.00

After the fluid component monitoring and concentration maintenancesystem has been installed, the reagents have been flushed and the systemsoftware reviewed, the fluid component monitoring and concentrationmaintenance system is ready for analysis service.

The Run Screen is shown in FIG. 19, and contains all data related to thecurrent analysis. This screen displays the concentration for samplesnumber 1 through 4 (if provided). It also displays the current/lastanalysis curve, which is generated in real-time during analysis.

Upon pressing [RUN], the analyzer will start its first analysis, thenrepeat at the interval specified in Setup Screen 4. If [SINGLE] ispressed, the analyzer will start a single analysis and, once finished,will remain idle until it receives a further command.

When the analyzer has started its analysis sequence, the upper rightcorner of the display, as illustratively shown in FIG. 20, indicates thecurrent step (“S1”) in the analysis sequence underneath the time. Duringthe analysis sequence, the [MAIN], [RUN], and [SINGLE] buttons are gone.At this time the analysis can only be interrupted by pressing the[RESET] button, which abruptly stops the analysis and returns theoperator to the Run Screen.

Underneath the sample concentration, which at this point reads 0.000, aline of text is displayed, indicating the function currently beingperformed. In this case “Taking Sample One” is displayed. The fluidcomponent monitoring and concentration maintenance system will gothrough the default sampling sequence and begin the titration.

Once the analysis is completed, the screen shown in FIG. 21 isdisplayed, identifying a water concentration of 2.343, which is thenumber of milliliters of titrant required to reach the endpoint. In thisillustrative example, no calculation factor has previously been enteredin Setup Screen 3.

Subsequent to display of numeric information as shown in FIG. 21, thefluid component monitoring and concentration maintenance system is readyto be calibrated to the associated semiconductor manufacturing process.The calibration process may comprise a “factor” calibration method,whereby the Calculation Factor is calculated from first principles, aspreviously discussed herein. Alternatively, a “process” calibration maybe performed, in which the analyzer is re-scaled to correlate with alaboratory analysis result.

A process calibration may be carried out in a “stop” mode. This is thesimplest way to perform a process calibration, but requires the fluidcomponent monitoring and concentration maintenance system to remainoff-line for the duration of the reference laboratory test procedure.The procedure is as follows:

-   -   Verify that the fluid component monitoring and concentration        maintenance system is running under normal process conditions,        and functioning correctly. If the process is not operating (i.e.        there is no sample flow), do not proceed with the calibration.    -   Press [SINGLE].    -   Take a grab sample during or immediately after the fluid        component monitoring and concentration maintenance system has        captured its sample for analysis. This ensures that the samples        are the same.    -   While the fluid component monitoring and concentration        maintenance system is completing its analysis procedure, subject        the grab sample to analysis using a reliable reference        laboratory method.    -   Once the fluid component monitoring and concentration        maintenance system has completed its analysis, advance to the        Sign-on Screen by pressing [MAIN]. Press [SETUP], then [NEXT]        until Setup Screen 3 is reached.    -   Set the Calibration Type parameter to “Process”.    -   Scroll [DOWN] to the appropriate Calculation Factor line (e.g.,        factor #1 for analysis #1, etc.). Press [ENTER], and dial in the        result of the laboratory analysis (in the appropriate units,        e.g. %, g/l, etc.). Once the last digit is entered, pressing        [ENTER] again will cause the fluid component monitoring and        concentration maintenance system to re-calculate the Calculation        Factor. Thus will be used in all subsequent measurements.    -   Exit the Setup Screens by pressing the [MAIN] key once. Press        the [RUN] key to return to the Run Screen. The displayed result        should now match the laboratory result previously entered.

An alternative procedure is to perform the process calibration in “run”mode, calibrating against a laboratory test performed while the fluidcomponent monitoring and concentration maintenance system remainson-line. This is particularly useful if the sample has to be sent toanother department or external laboratory for analysis. The procedure isas follows:

-   -   Verify that the fluid component monitoring and concentration        maintenance system is running under normal process conditions,        and functioning correctly. If the process is not operating        (i.e., there is no sample flow), do not proceed with the        calibration.    -   The fluid component monitoring and concentration maintenance        system will likely be in Run mode, so wait until the next        analysis cycle begins.    -   Take a grab sample during or immediately after the fluid        component monitoring and concentration maintenance system has        captured its sample for analysis. This ensures that the samples        are the same.    -   Once the fluid component monitoring and concentration        maintenance system has completed its analysis, record the        displayed result, as displayed result “C1”.    -   Analyze the grab sample using a reliable reference laboratory        method. Record the laboratory test result, as result “A1.”    -   Exit the fluid component monitoring and concentration        maintenance system Run mode by pressing the [STOP] key (visible        between analysis cycles). Record the fluid component monitoring        and concentration maintenance system's currently displayed        result, as displayed result “C2”.    -   Advance to the Sign-on Screen by pressing [MAIN].    -   Advance to Setup Screen 3 by pressing [SETUP] then [NEXT] twice.    -   Calculate the “adjusted calibration value” (CAL) as follows:        CAL=(A1/C1)×C2    -   Set the Calibration Type parameter to “Process”.    -   Scroll [DOWN] to the appropriate Calculation Factor line (e.g.,        factor #1 for analysis #1, etc.). Press [ENTER], and dial in the        CAL value. Once the last digit has been entered, pressing        [ENTER] again will cause the fluid component monitoring and        concentration maintenance system to re-calculate the Calculation        Factor. This will be used in all subsequent measurements.    -   Exit the Setup Screens by pressing the [MAIN] key once. Press        the [RUN] key to return to the Run Screen. The displayed result        should now match the CAL value previously entered.

This calculation protocol is intended to compensate for possible changesin the process chemistry between the time the grab sample was taken andwhen the Calculation Factor is updated.

An illustrative example is set out below.

EXAMPLE

The analyzer's displayed result at the time of the grab sample was 3.863wt % (C1).

Laboratory analysis reports the concentration of the grab sample to be4.101 wt % (A1).

The analyzer's displayed result at the time of updating the calibrationis 3.422 wt % (C2)CAL=(4.101/3.863)×3.422=3.633

Therefore, the adjusted calibration value (CAL) is 3.633 wt %.

Set out below is an identification of error codes of the AnalyticalInformation Module of the fluid component monitoring and concentrationmaintenance system, such as may be encountered in the operation of theapparatus, together with a tabulation of the meanings and severity ofsuch error codes. error code meaning severity 1 The sample is alreadyneutral (detection in single Fatal: Analyzer will not proceed withendpoint inflection point mode) analysis until problem is corrected 2The sample is already neutral (detection of first endpoint Fatal:Analyzer will not proceed with in dual inflection point mode) analysisuntil problem is corrected 4 The sample is already neutral (detection ofsecond endpoint Fatal: Analyzer will not proceed with in dual-inflectionpoint mode) analysis until problem is corrected 8 Too many data points(increments too small) Warning: Accurate detection of endpoint may notbe possible 16 Calculation of results impossible (incompatible outputFatal: Analyzer will not proceed with assignments) analysis untilproblem is corrected 32 Process calibration received invalidconcentration data Warning: Analysis proceeds using old data

In one embodiment of the invention, multiple error-states are indicatedby a composite error code. To decode, simply subtract the highest errorcode possible and keep doing so until 0 is reached. For example,E40=E32+E8.

The correlation of real-time analysis curves and error codes provides aconjoint analytical approach to analysis of the fluid componentmonitoring and concentration maintenance system performance.

The real-time analysis curves can be utilized as a “fingerprint” for aparticular analysis. Interpretation of error codes should be done inconjunction with an evaluation of the curve shape. The ensuingdiscussion is directed to the relationship between the error codes andthe curve shape.

Curve 1 is shown in FIG. 22. This rapid change in sensor mV suggests alack of sample.

The first small amount of titrant, when added to the pure solvent,causes the sensor response to jump immediately to the titre end. Thismay be accompanied by an E1 error code. The calculated results wouldmost likely be very low (or even 0).

In this case, check that the sample is being delivered from the processto the reaction vessel correctly.

Curve 2 is shown in FIG. 23. A “flat” sensor response like this can havetwo causes.

First, if the sensor mV is in an unexpected range, then this mayindicate a faulty sensor, connection, pre-amp or other electronic fault.

On the other hand, if the sensor mV remains in the normal pre-endpointrange, then reagent may not be reaching the reaction vessel. This wouldtypically be accompanied by an E8 error code. The level of reagentsshould be checked, and it should be verified that the burette is filledand functioning properly.

Curve 3 is shown in FIG. 24. This scenario usually occurs when theendpoint interpretation parameters have been changed within the SetupScreens, but the chemistry remains the same.

In this case, the Setup parameters should be carefully reviewed, and thepasscode feature is desirably employed to safeguard Setup parametersfrom unauthorized access.

Another cause can be a sensor that has drifted out of the normalendpoint window. If the Setup parameters are correct, the sensor shouldbe cleaned or replaced as necessary.

After an analysis is finished, the analyzer will display an [OPTIMIZE]menu option in the Run Screen, as shown in FIG. 25. This feature allowsfor the optimization of the endpoint and the minimum and maximumincrements used.

To use the Optimize Screen, press [OPTIMIZE]. This will generate thescreen shown in FIG. 26.

This screen allows selection of the endpoint with the greatest gradient(strongest point of inflection), and thus optimization of the endpointand increments to find this endpoint every time. In the above case, [UP]is pressed until the 0.36/750/265.30 line is at the top, then [SELECT]is pressed. The Setup parameters then are automatically optimized to theselected point. Care should be exercise with this procedure, since if aninappropriate endpoint is selected, the Setup parameters will beinadvertently changed, and will adversely impact the analysis accuracy.

The fluid component monitoring and concentration maintenance system ispreferably maintained on a regular maintenance schedule, involvingreplenishment of reagents, replacement of burette O-rings, updating ofAnalytical Information Module software, refurbishing/replacement ofelectrodes, etc.

While the invention has been described herein with primary reference tothe use of Karl Fischer titration techniques in respect of monitoringand control of water in semi-aqueous solvent media, it will beappreciated that the invention is susceptible of use with otheranalytical techniques and chemistries, and/or for monitoring and controlof other fluids than semi-aqueous solvent media, and/or for monitoringand control of other fluid components than water.

In lieu of the specifically described methodology for monitoring andcontrolling the concentration of the water component of a sample usingthe classic Karl Fischer titration methodology, alternative methods ofanalysis that can also be used include spectroscopic analysis ofinfrared and near infrared frequency fluctuations, measurement ofvariations in the multicomponent solution conductivity, and the use ofultrasonic wave generation, e.g., involving impingement of ultrasonicenergy on the sample liquid, and measurement of the response of thesample thereto.

By way of further specific examples, the method of the invention may bepracticed with ultraviolet-visible detection and monitoring of liquidspecies in liquid multicomponent compositions, or withmicroelectromechanical devices (MEMs) for detection and monitoring ofgas species of multicomponent gas compositions, thermopile device-baseddetection and monitoring of gaseous species in a multicomponent gascomposition, and electrochemical cells of varied types for detection andmonitoring of liquid species of multicomponent liquid compositions.

The invention in application to water monitoring and control ofsemi-aqueous solvent media thus provides an apparatus and method forextracting small amounts of the clean chemistry, such as solventmixtures used for photoresist and post-etch residue removal, measuringthe water content of the clean chemistry, and responsively injectingadditional water as necessary to maintain water concentration withinappropriate levels. In solvent compositions based on NPM, the amount ofwater in the chemistry is a critical feature in determining bathlife. Ifthe water level in the solvent composition is too low, the cleaningefficiency will be reduced. If the water level is too high, there is astrong risk of metal corrosion. It therefore is critical to maintainwater level within a strict range of concentration. When the water levelis appropriately maintained, the bathlife can be extended substantially,e.g., 2-3 times, beyond the level achievable without monitoring andwater control concentration maintenance. The increased bathlife reduceschemical usage and chemical waste, as well as the need for downtime tofacilitate chemical changeouts. Additionally, the increased bathlife andassociated maintenance of the value of the water concentration in thesolvent composition enables tight process control and higher yields tobe realized.

The water monitoring and control apparatus and method of the inventionthus effects injection of water into semi-aqueous solvent mixtures asneeded to maintain a predetermined level of water concentration in thesolvent composition for maximizing its efficiency.

The invention embodies a real-time chemical bath monitoring andreplenishment system, which may be usefully employed in a wide varietyof applications, including semiconductor manufacturing operations suchas photoresist and post-etch residue removal from semiconductor devicestructures and precursor articles, chemical-mechanical planarization inwhich solvent components ratios in the CMP composition are critical tothe material removal operation, as well as other applications in whichone or more solvent components of a multi-component composition aresusceptible to analytical assessment and monitoring.

In another aspect of the invention, there is provided a means and methodof generating and monitoring species such as H₂O₂.

Hydrogen peroxide (H₂O₂) used in semiconductor processes is typically ofunknown concentration due its spontaneous decomposition into water overtime.

The present invention in a specific embodiment resolves such problem, bycarrying out electrochemical generation of high purity peroxide at thepoint of use, and performing real time quantitative analysis of theperoxide as it is generated and in the process in which it is beingused.

The generation of hydrogen peroxide in accordance with such aspect ofthe invention is carried out by electrochemical means. Suchelectrochemical generation of hydrogen peroxide is extremely efficient.For example, hydrogen peroxide can be generated in an electrochemicalcell, e.g., to produce at least 0.054 mol of peroxide in a basic mediumof sodium hydroxide using only 150 mA.

A Karl Fisher dual electrochemical cell (e-cell) arrangement may be usedas the platform in conjunction with a constant current source with aAg/AgCl reference electrode. The working electrode (cathode in thiscase) connected to the current source can be constituted by a sinteredcarbon/PTFE composite disk in intimate contact with a nichrome screen.This electrode is highly porous and as such allows oxygen to diffusethrough at a rapid rate to promote the formation of peroxide at thecathode. The anode material can be graphite or Pb/PbO₂ prepared asdescribed in Brillas, E., J. Electrochem Soc., 142 (1995) 1733, thedisclosure of which hereby is incorporated herein by reference in itsentirety. In basic solution this cathode configuration will catalyze atwo-electron reduction of oxygen to peroxide via the hydroperoxideanion:O₂+H₂O+2e=HO2⁻+HO⁻.

Transition metal catalysts may also be added to facilitate the reductionprocess and to increase peroxide yield or improve the reactionefficiency.

The equipment configuration for this generation of hydrogen peroxide andmonitoring of same may be advantageously carried out in the equipmentconfiguration shown in FIG. 27, utilizing a Karl Fischer analysis tray.The top cell is used for the generation of the peroxide and a smallaliquot is removed using the syringe pumps and shuttled to the cellbelow where it can be tested using permanganate or ceric ammoniumsulfate. The bulk of the peroxide generated can be shuttled to a holdingvessel by pressurizing the cell.

The top cell uses two platinum electrodes that are easily modified tohold a Pb/PbO₂ electrode and a composite graphite/Teflon electrode.

Peroxide concentration, e.g., in chemical mechanical planarization (CMP)slurries employed in semiconductor manufacturing processes for polishingof semiconductor devices and device precursor structures, can be easilymonitored by titrating with permanganate or ceric ammonium sulfate.Other transition metal salts may be used with corresponding advantage,e.g., Fe complexes such as NH₄Fe(oxalate), NH₄Fe(sulfate) orNH₄Fe(nitrate), to carry out the following reactions:2Fe+2e ⁻=2Fe⁺²2Fe⁺²+2O⁻=O₂+2Fe⁺³

FIG. 28 is a graph of titrant volume as a function of titration cyclesusing ceric ammonium sulfate, and showing the reproducibility of 2.5%peroxide determination.

The half reactions for the titration of H₂O₂ with standard Ce^(+4 are:)2Ce⁺⁴+2e ⁻→2Ce⁺³2O⁻→O₂+2e ⁻

The complete reaction for this titration is:2Ce⁺⁴+2O⁻→O₂+2Ce^(+3.)

The invention in another aspect relates to the generation and monitoringof hydrazine and hydroxylamine.

Hydroxylamine and hydrazine are used as active reagents in severalsemiconductor processing operations. However, both chemicals present atransport and storage problem due to their explosive nature and highreactivity. In-situ generation is highly advantageous as solidhydroxylamine is known to rapidly detonate when dried.

The present invention resolves the aforementioned difficulties by (i)electrochemical generation of these compounds at their point of use,(ii) simultaneous real-time process monitoring of the concentration ofthese chemicals both in the electrochemical cell and at the point ofuse, and (iii) use of a modified Karl Fisher electrochemical cellplatform for both the generation and monitoring of these compounds.While described below in reference to hydroxylamine, it will beappreciated that corresponding procedures may be employed for thegeneration and monitoring of hydrazine in accordance with the invention.

The electrosynthesis of hydroxylamine by be effected by reductionreaction in mild nitric acid solutions at a mercury amalgam electrode:NO₃ ⁻+7H⁺+6e ⁻=H₂NOH+2H₂O

Alternatively, glassy carbon electrodes with a thin polymer membrane,formed from polyphenylenediamine in nitric acid, can be used to promotethis reaction and suppress further reduction to ammonia. Typical currentdensities are under 1 A/cm².

Using a Karl Fisher platform or a similar electrochemical cell platform,hydroxylamine can be generated in one cell, a small aliquot shuttled tothe second cell, and an analysis performed to detect the presence andconcentration of hydroxylamine. Likewise, sample from the process(utilizing the hydroxylamine) can be taken on board the analysis toolvia a six port valve and analyzed in a similar manner, preferably in anautomated manner.

Since hydroxylamine is reducible to ammonia at a platinum electrode,subsequent titration with an oxidizer such as permanganate can bemonitored with an oxidation-reduction potential (ORP) electrode.

Another potential synthetic method for generating hydroxylamine bubblesboth NH₃ and O₂ gas into an aqueous solution in an electrochemical cell,as described herein. Transition metal catalysts may also be added toenhance the reaction efficiency and to increase the overall yield offormation.

A dual cell apparatus of the type as shown in FIG. 28 may be employedwherein the top cell is utilized to monitor sample from the process bathor the lower cell for hydroxylamine concentration.

Although the invention has been variously disclosed herein withreference to illustrative embodiments and features, it will beappreciated that the embodiments and features described hereinabove arenot intended to limit the invention, and that other variations,modifications and other embodiments will suggest themselves to those ofordinary skill in the art. The invention therefore is to be broadlyconstrued, consistent with the claims hereafter set forth.

1. A multicomponent fluid composition monitoring and compositionalcontrol system, said monitoring and compositional control systemcomprising: (a) a tank containing the multicomponent fluid composition;(b) a recirculating system, wherein said multicomponent fluidcomposition is withdrawn from the tank and circulatingly flowed throughat least a pump and a filter and returned to the tank; (c) an analyzerunit comprising a sampling system and a reagent dispensing system,wherein said analyzer unit is constructed and arranged to monitorconcentration of at least one component of the multicomponent fluidusing a real-time methodology comprising spectroscopic analysis ofnear-infrared frequency fluctuation; (d) a by-pass loop positioneddownstream of the pump and the filter, wherein the multicomponent fluidis bled from the recirculating system to the analyzer unit for analysistherein; and (e) a control unit, constructed and arranged to compare theresults of the real-time methodology to pre-programmed specificationsand responsively control dispensing of said at least one component froma source of said component into the multicomponent fluid using thereagent dispensing system to maintain the concentration of said at leastone component in the multicomponent fluid, wherein the multicomponentfluid is utilized in a fluid-using processing facility.
 2. The system ofclaim 1, wherein said processing facility comprises a semiconductormanufacturing facility.
 3. The system of claim 2, wherein thesemiconductor manufacturing facility comprises a process selected fromthe group consisting of etching, chemical mechanical planarization(CMP), photolithography, chemical vapor deposition, spin-on coatingsapplication, supercritical fluids cleaning operations, wafer solventdrying operations, and photoresist and post-etch residue removal.
 4. Thesystem of claim 1, wherein the multicomponent fluid comprises asemi-aqueous solvent medium.
 5. The system of claim 1, wherein thecontrol unit includes computational means and a display for visualobservation of outputted data of the unit.
 6. A multicomponent fluidcomposition monitoring and compositional control system, said monitoringand compositional control system comprising: (a) an analyzer unitcomprising a sampling system and a reagent dispensing system, whereinsaid analyzer unit is constructed and arranged to monitor concentrationof water in the multicomponent fluid using a real-time methodologyselected from the group consisting of a Karl Fischer titration,measurement of multicomponent fluid conductivity, and ultrasonic energyresponse of the multicomponent fluid; and (b) a control unit,constructed and arranged to compare results of the real-time methodologyto pre-programmed specifications and responsively control dispensing ofwater from a source of water into the multicomponent fluid using thereagent dispensing system to maintain the concentration of water in themulticomponent fluid, wherein: the multicomponent fluid is utilized in afluid-using processing facility; and the sampling system is arranged tocapture a sample deriving from a flow stream of said multicomponentfluid.
 7. The system of claim 6, wherein said processing facilitycomprises a semiconductor manufacturing facility.
 8. The system of claim7, wherein the semiconductor manufacturing facility is adapted toconduct a process selected from the group consisting of etching,chemical mechanical planarization (CMP), photolithography, chemicalvapor deposition, spin-on coatings application, supercritical fluidscleaning operations, wafer solvent drying operations, and photoresistand post-etch residue removal.
 9. The system of claim 8, wherein thesemiconductor manufacturing facility is adapted to conduct a process forphotoresist and post-etch residue removal.
 10. The system of claim 6,wherein the multicomponent fluid comprises a semi-aqueous solventmedium.
 11. The system of claim 6, wherein the multicomponent fluidcomprises water and organic solvent components.
 12. The system of claim6, wherein the semi-aqueous solvent medium comprises water and aphotoresist stripping solvent.
 13. The system of claim 6, wherein thesampling system is arranged to capture a sample from a by-pass loop of aflow stream of said multicomponent fluid.
 14. The system of claim 6,wherein the real-time methodology comprises the measurement ofmulticomponent fluid conductivity.
 15. The system of claim 6, whereinsaid analyzer unit further comprises a bath of said multicomponent fluidfrom which sampling is conducted using the analyzer unit, and from whichfluid is withdrawn from and flowed to the fluid-using processingfacility.
 16. The system of claim 6, wherein the analyzer unit isconstructed and arranged to conduct a Karl Fischer titration of thefluid withdrawn from the bath.
 17. The system of claim 6, wherein thepre-programmed specifications include volume of the bath beingmonitored, frequency of monitoring and a titration calculation factorfor calibration.
 18. The system of claim 6, comprising a source oftitration reagent(s) for conducting the Karl Fischer titration.
 19. Thesystem of claim 6, comprising a dryer adapted for conductingpre-titration drying of at least one reagent for conducting the KarlFischer titration.
 20. The system of claim 6, further comprising aconstant-current module adapted for detection of the endpoint of theKarl Fischer titration.